Sensor element with a memory for abnormal changes of the incident light intensity

Abstract

A sensor element with a memory for changes of the incident light intensity. The sensor element comprises a light-sensitive element connected in series with a fixed resistor, and a light modulator shunted either across the light-sensitive element or the resistor. The light modulator influences the incidence of light onto the light-sensitive element. The reflection, absorption and/or transmission behavior of the light modulator changes as a function of the applied voltage or the current. The sensor element according to the invention has the advantage that it can be manufactured simply and cost-effectively so that it is also suitable for use in large arrays.

What is claimed is: 
     
       1. A sensor element having a memory for changes of the incident light intensity, comprising a light-sensitive element connected in series with a resistor, either the light-sensitive element or the resistor being shunted by a light modulator which influences the light incident on the light-sensitive element, said modulator having a reflection, absorption and/or transmission behavior which changes as a function of the voltage applied to the modulator or the current through the modulator. 
     
     
       2. The sensor element recited in claim 1, wherein the light modulator is arranged in front of the light-sensitive element. 
     
     
       3. The sensor element recited in claim 1 wherein the light modulator comprises a liquid-crystal element. 
     
     
       4. The sensor element recited in claim 1, wherein the light-sensitive element comprises a photodiode biased in the backward direction. 
     
     
       5. The sensor element recited in claim 1, wherein, for the storage of light flashes or light failure, the light modulator reflects the inncident light if the applied voltage is high, and is connected in parallel with the light-sensitive element. 
     
     
       6. The sensor element recited in claim 1, wherein the light modulator reflects the incident light if the applied voltage is low, and is connected in parallel with the resistor, thereby providing storage for incident light flashes. 
     
     
       7. The sensor element recited in claim 7, wherein the light-sensitive element and the resistor are fabricated by a thin-film technique. 
     
     
       8. An electronic drawing board in which drawings are generated by a light stylus directed at the board, information generated by the board being transmittable to an information receiving device, for example, a computer, the board comprising a plurality of sensor elements arranged on a common substrate, each of said sensor elements comprising a light-sensitive element connected in series with a resistor, either the light sensitive element or the resistor being shunted by a light modulator which influences the light incident on the light-sensitive element, said modulator having a reflection, absorption and/or transmission behavior which changes as a function of the voltage applied to the modulator or the current through the modulator. 
     
     
       9. The electronic drawing board recited in claim 8, wherein the light modulator is arranged in front of the light-sensitive element. 
     
     
       10. The electronic drawing board recited in claim 8 wherein the light modulator comprises a liquid-crystal element. 
     
     
       11. The electronic drawing board recited in claim 8, wherein the light-sensitive element comprises a photodiode biased in the backward direction. 
     
     
       12. The electronic drawing board recited in claim 8, wherein, for the storage of light flashes or light failure, the light modulator reflects the incident light if the applied voltage is high, and is connected in parallel with the light-sensitive element. 
     
     
       13. The electronic drawing board recited in claim 8, wherein the light modulator reflects the incident light if the applied voltage is low, and is connected in parallel with the resistor, thereby providing storage for incident light flashes. 
     
     
       14. The electronic drawing board recited in claim 8, wherein the light-sensitive element and the resistor are fabricated by a thin-film technique.